1. Field of the Invention
This invention relates to a racket stringing apparatus whereby rackets, such as tennis rackets, can be strung quickly under an appropriate tension so as to provide a superior playing quality to the rackets.
2. Description of the Related Art
The improvement of this invention is directed to a conventional racket stringing apparatus which is shown in FIG. 1 and which includes a metal base plate 1, a racket retaining device 2, a rectangular casing 3 and a string tautening device 4. As illustrated, the base plate 1 has an outline of a racket and has a fixed upright shaft 10 which has several circumferentially aligned horizontal positioning holes 101 formed in the peripheral surface of the base plate 1.
The racket retaining device 2 includes a support plate 20 having a downward flange 201 which is shaped in the form of a hollow cylinder and which is sleeved on the upper end portion of the shaft 10. The flange 201 has a horizontal positioning hole 202 formed therethrough so that a horizontal positioning pin 203 extends through said positioning hole 202 of the flange 201 into selected one of the positioning holes 101 of the shaft 10. A set of retainer units 21 are disposed on the support plate 20. The distance between the retainer units 21 can be adjusted to retain effectively a racket (not shown) thereon.
The casing 3 is fixed on the base plate 1 and has an open top end and an internal space 30. A notch 31 is formed in the upper end of a wall of the casing 3. As shown in FIG. 2, the string tautening device 4 includes a rotary element 40 mounted rotatably within the casing 3 by a pivot pin 401, an inverted U-shaped hollow lower clamping member 41 riding and pivoted to the rotary element 40, and an upper clamping member 42 mounted movably on the lower clamping member 41 and having two flanges 421, 422 projecting from two opposite sides of the upper clamping member 42. A coiled spring 43 is received in the lower clamping member 41. Two metal washers 44 respectively abut against the upper and lower ends of the spring 43, and are respectively pushed by the spring 43 to the upper and lower ends of the internal space of the lower clamping member 41. An impelling rod 45 has a lower end pivoted to the rotary element 40 by a pivot pin 451, an upper end secured to the upper clamping member 42 by a positioning pin 452, and an intermediate portion extending through the spring 43 and the washers 44. An inclined swing lever 46 is secured in the cylindrical hole 402 of the rotary element 40 by a positioning pin 461 and has a series of marks (see FIG. 1) indicated on the lever 46. A counterweight 47 (see FIG. 1) is mounted movably on the lever 46 so as to adjust the force to tauten the string 5 which is to be strung on the racket (not shown). An elongated blocking member 48 is mounted rotatably in the casing 3 by a pivot pin 481 at the upper portion thereof so that action of gravity locates the blocking member 48 at an inclined normal position, where the upper end of the blocking member 48 presses against the concaved portion 403 of the rotary element 40, with the result that the swing lever 46 cannot be turned downward. A push rod 482 is attached to the blocking member 48 and has an outer end (see FIG. 1) which is exposed to the exterior of the casing 3 and which can be moved to the release position indicated by the phantom lines so as to separate the blocking member 48 from the rotary element 40, thereby enabling the swing lever 46 to be turned downward. Accordingly, the swing lever 46 can be maintained at the inclined normal position unless the push rod 482 is actuated to separate the blocking member 48 from the rotary element 40.
Referring to FIG. 3, in operation, when one desires to string a racket (not shown), the swing lever 46 is turned upward so as to move the impelling rod 45 upward. Upward movement of the impelling rod 45 separates the lower end of the upper clamping member 42 from the upper end of the lower clamping member 42, so as to form a string receiving gap 49 between the upper clamping member 42 and the lower clamping member 41. Referring to FIG. 4, the string 5 is passed through the gap 49 in such a manner that it is pressed against two opposite sides of the impelling rod 45 and of the right flange 421 and extends around the left portion of the left flange 422. Then, referring to FIG. 2, the push rod 482 is moved to the release position indicated by the phantom lines so as to separate the blocking member 48 from the rotary element 40. Subsequently, a hand of the operator holds the portion 52 (see FIG. 4) of the string 5 which extends from the lower side of the right flange 421, while the other hand turns the swing lever 46 downward so as to move the lower end of the upper clamping member 42 toward the upper end of the lower clamping member 41, thus clamping tightly the string 5 between the upper clamping member 42 and the lower clamping member 41 and dividing the string 5 into a tautened section 51 and a non-tautened section 52. At this time, if the swing lever 46 is in a horizontal position, the tension of the tautened section 51 of the string 5 is appropriate. Otherwise, the tautened section 51 of the string 5 is loosened and the above operation procedure is repeated in such a manner that the position of the swing lever 46 is changed until it is in a horizontal position.
The conventional racket stringing apparatus suffers from the following disadvantages:
1. The steps of clamping the string 5 between the upper clamping member 42 and the lower clamping member 41, and of actuating the swing lever 46 and the push rod 482 to adjust the tension to tauten the string 5, are time-consuming.
2. Because the positions of the positioning holes 101 of the shaft 10 cannot be seen by the operator, the step of passing the positioning pin 203 through the positioning hole 202 of the flange 201 and into selected one of the positioning holes 101 of the shaft 10 is time-consuming and troublesome.
3. Because there is no means for preventing the swing lever 46 from moving to a level below the bottom surface of the base plate 1, when the blocking member 48 separates from the rotary element 40 in an undesired condition, the actuator end of the swing lever 46 may strike on the ground, causing damage and reduced-straightness of the swing lever 46. This reduction of the straightness decreases the precision of the apparatus.
4. The apparatus is too bulky to have a convenient transportation and storage.